The present invention relates generally to a method for producing an aluminum alloy suitable for elevated temperature applications by controlled solidification that combines composition design and solidification rate control to enhance the aluminum alloy performance.
Gas turbine engine components are commonly made of titanium, iron, cobalt and nickel based alloys. During use, many components of the gas turbine engine are subjected to elevated temperatures. Lightweight metals, such as aluminum and magnesium and alloys of these metals, are often used for some components to enhance performance and to reduce the weight of engine components. A drawback to employing conventional aluminum alloys is that the strength of these alloys drops rapidly at temperatures above 150 ° C., making these alloys unsuitable for certain elevated temperature applications. Current aluminum alloys, either wrought or cast, are intended for applications at temperatures below approximately 180° C. (355° F.) in the T6 condition (solution treated, quenched and artificially aged).
Several high temperature aluminum alloys have been developed, but few product applications exist despite the weight benefits. This is partially because of the slow acceptance of any new alloy in the aerospace industry and also because high temperature aluminum alloys have fabrication limitations that can counter their adoption for production uses. Many of the potential components for which high temperature alloys could be used are produced using welding, brazing or casting. Fabrication of these components using wrought high temperature aluminum alloys (including powder metallurgy routes) may be possible, but the cost often becomes prohibitive and limits production to very simple parts. Conversely, it is difficult to develop high temperature property improvements in aluminum alloys that are fabricated into complex shapes by conventional casting, the least expensive process.
Recently, there have been improvements in the casting technology of aluminum alloys, e.g., aluminum-silicon based alloys such as D-357. These improvements have allowed for “controlled solidification” of aluminum-silicon alloys, similar to those improvements achieved in the liquid-metal cooling of directional/single crystal superalloys. This can provide considerable refinement and uniformity of grain and precipitate morphologies to improve the combined strength and ductility consistently throughout the casting. This provides a robust quality to the properties that component designers need in current alloy compositions, such as D-357. However, these alloys do not meet the level of properties needed for higher temperature applications. New composition designs are needed that combine synergistically with controlled solidification technology to significantly increase the high temperature capabilities.
Hence, there is a need in the art for a method for producing an aluminum alloy by controlled solidification that combines composition design and solidification rate control, that is designed to synergistically enable the production of complex cast components for high temperature applications (e.g., gas turbine and automotive engine components and structures) and that overcomes the other shortcomings and drawbacks of the prior art.